A variety of consumer products include a heating element or heating body that is used to produce heat. The heating body has a positive temperature coefficient to allow for temperature control. Electronic products with a heating body are now widely used in people's daily life. Such products include a hair curler, a hair-straighter, an electric blanket, and many other kinds of products.
In these products, the heating body is both the heating element and the temperature sensor. The positive temperature coefficient allows the heating body itself to function as the temperature sensor, so an additional temperature sensor is not needed. These heating products that have a heating body that functions as both the heat generator and the temperature sensor are referred to as sensorless products. Sensorless products have many advantages, including a compact size and control structure, stable temperature performance, safety, and better robustness for daily use.
Older sensorless products may use a conventional temperature-measuring circuit. A conventional temperature-measuring circuit has a sampling circuit, a reference circuit, and a voltage comparator. To prevent damage to an integrated circuit (IC) from high voltages, a diode is inserted in series in the sampling circuit.
Unfortunately, the forward voltage drop of the diode creates an inaccuracy due to the temperature-drift characteristics of the diode. Conventional circuits generally ignore this error, which can cause an error in the temperature control. A technical problem is that the temperature-measuring result of the conventional method in sensorless products can vary with ambient temperature.
What is desired is to solve this temperature-control problem caused by the diode that prevents circuit damage caused by high voltages. It is desired to make accurate measurements without the effect of ambient temperature variation. A solution is desired that can be implemented by an integrated circuit with a compensation diode and a resistor. Compensation of measurement error for the full temperature range of the products is desirable.